Metal periodates are unstable in acid or alkaline solutions. For this reason it has not previously been possible to use such materials as depolarizers for conventional acid or alkaline primary or secondary cells.
The object of this invention is to provide novel electrode chemical energy generators with:
A. HIGH VOLTAGES,
B. HIGH ENERGY DENSITIES,
C. HIGH MATERIAL UTILIZATION EFFICIENCIES
D. NO SPONTANEOUS GASING
This invention is based upon the use, as active cathode material of the oxy acids of iodine in the form of metal salts with certain heavy metals. The periodates of copper, silver, iron, cobalt, and mixtures thereof are particularly suitable as depolarizers for this invention. Such active cathodic materials are used in conjunction with nonaqueous electrolytes in electrochemical generators. The electrochemical generators for the utilization of such active materials include, as anodic material, active light metals preferably of the type of lithium, sodium, potassium, etc.
Within the ambit of this invention are the novel active cathodic materials; cathodes prepared from such novel cathodic material; methods of making such cathodes from said active materials and the complete electrochemical generators using such active cathodic and anodic materials in conjunction with non-aqueous electrolytes. Broadly stated according to the principles of the present invention, there is provided an electric cell comprising a light metal anode, a heavy metal periodate cathode, and an organic electrolyte.
Light metals suitable for the purpose of the present invention are selected from among lithium, sodium, potassium, beryllium, calcium, magnesium, and aluminum. In some cases, it is desirable to amalgamate the surface of the anode metal with mercury as the performance of certain light metal anodes for such cells can be considerably improved by such amalgamation. By surface alloying these metals with mercury by chemical displacement of the latter from solutions of a mercury salt, a notable improvement of the anodes is provided. The improvement is particularly striking with anodes formed of aluminum, magnesium, or their alloys. Amalgamation may be successfully carried out by bringing the anode metal into contact with mercuric salts dissolved in N:N dimethyl formamide, gamma-butyrolactone, acetone or in other suitable solvents. Among useful mercuric salts for such solution are mercuric chloride, mercuric nitrate, mercuric acetate, mercuric chlorate, mercuric bromide and mercuric thiocyanate. Generally speaking the principles of selection of a suitable system (solute-solvent) for amalgamation of the following:
a. The mercury salt should be soluble in the solvent.
b. The anion of the mercury salt should form salts with the anode metal, that are also soluble in the solvent employed to dissolve the mercury salt.
c. The solvent should be stable in the presence of the anode metal and its amalgam, more particularly it should not decompose evolving hydrogen, as would be the case with acetic acid.
The active metal anodes are amalgamated to reduce local action on the anode surface thus providing consistant and reproduceable electrochemical results. Specifically it has been noted, with aluminum and magnesium anodes, that amalgamation assures elimination of the usual time lag for initiation of the current flow. With anodes of such metals and their alloys the usual time lag is reduced to less than 10.sup.-3 seconds.
The novel cathodic material or depolarizers used in the present invention are the heavy metal salts of the oxy acids of iodine. The periodates (IO.sub.6.sup.-5) of copper, silver, iron, cobalt, nickel, mercury, thallium, lead, and bismuth and mixtures thereof are particularly suitable as the active cathodic or depolarizer materials for cells to be used in conjunction with the above mentioned active light metal anodes. The silver periodate, Ag.sub.5 IO.sub.6 is preferred.
Suitable electrolytes may be made by dissolving organic or inorganic salts of light metals in the organic solvents. For example, 1-2 Molar solutions of lithium perchlorate, or lithium aluminum chloride dissolved in tetrahydrofuran solvent constitute a suitable organic electrolyte. Other light metal salts are based upon the cations of the light metals such as lithium, sodium, beryllium, calcium, magnesium or aluminum with anions such as perchlorate, tetrachloroaluminate, tetrafluoroborate, chloride, hexafluorophosphate, hexafluoroarsenates, etc. dissolved in organic solvents. Among suitable organic solvents are tetrahydrofuran, propylene carbonate, dimethyl sulfide, dimethyl sulfoxide, N-nitrosodimethylamine, gamma-butyrolactone, dimethyl carbonate, methyl formate, butyl formate, acetonitrile and N:N dimethyl formamide.
This invention in addition to the electrochemical system mentioned above also contemplates cells and batteries utilizing this system which are simple in construction reliable and safe in operation, and which may be readily manufactured and sold on a practical and commercial scale at a low cost. Similarly included within the ambit of this invention is the method of manufacture of the cathodes from the cathodic materials.